Oligomerization of light olefins is a well-known process which utilizes different catalytic system for production of various desired end products. Oligomerization of isobutene particularly dimerization of isobutene is important for production of high octane gasoline blending component. Dimerization of isobutene is a well-known side reaction in the MTBE production process and highly exothermic. In order to avoid the formation of dimer, methanol is always kept in excess to the stoichiometric ratio required for MTBE production. By reducing the methanol to isobutene mole ratio one can produce both the dimer product and MTBE in the same reactor.
EP 1074534 utilizes similar kind of process as MTBE production, which adds fresh methanol, MTBE, MSBE, secondary butyl alcohol and mixture thereof at different mole ratios along with the refinery C4 feedstock containing isobutene to the reactor employing an oligomerization catalyst. As there are more number of alcohols and ethers added as fresh feedstock the cost for production of dimer product will grow up and it will affect the economics of the process when comes into the industrial application point of view.
In oligomerization reaction using ion exchange resin as catalyst, particularly in dimerization of isobutene to isooctene, various polar compounds are used as selectivity enhancer for dimer product. Tertiary butyl alcohol (TBA) is one such polar component widely used in the dimerization process as selectivity enhancer.
TBA is one of the costliest chemicals which is produced commercially through well-known Oxirane process as described in U.S. Pat. No. 3,351,635. Some of the patents like U.S. Pat. No. 8,067,655, WO03/033442 made the efforts to recover the alcohol especially TBA using the energy intensive and cost intensive process like extraction, dual distillation etc. as the TBA cannot be recovered easily owing to its azeotrope formation with water.
In situ production of TBA in a dimerization reactor as disclosed in U.S. Pat. No. 4,100,220, WO 2010/065234, will make the progress of both the reaction competitive and yield undesired product selectivity w.r.t TBA and dimer. This is because both the reactions require different reaction environment which cannot be maintained in a single reactor.
US 2007/0083069 describes a process for selective oligomerization of isobutene to di-isobutene in presence of TBA as selectivity enhancing modifier. The said modifier is prepared in a separate reactor and the substantially free of water modifier is separated and sent to oligomerization reactor where isobutene reacts in the presence of said separated modifier to selectively form di-isobutene. No clear description for the method of separation of the modifier has been given in this application.